Dynamic random access memory (DRAM) capable of canceling out complimentary noise development in plate electrodes of memory cell capacitors

ABSTRACT

Disclosed herein is a dynamic RAM comprising a plurality of word lines respectively connected to address select terminals of a plurality of dynamic memory cells, a plurality of complementary bit line pairs respectively connected to input/output terminals of the plurality of dynamic memory cells and placed in directions opposite to one another, and a sense amplifier array which is supplied with an operating voltage according to an operation timing signal and comprises a plurality of latch circuits for respectively amplifying the differences in voltage between the complementary bit line pairs. In the dynamic RAM, common electrodes provided in opposing relationship to storage nodes corresponding to connecting points between address select MOSFETs and information storage capacitors of the plurality of dynamic memory cells provided on both sides with the sense amplifier array as the center are connected to one another while circuit connections in the sense amplifier array are being ensured by wiring means using the common electrodes.,

BACKGROUND OF THE INVENTION

The present invention relates to a dynamic RAM (Random Access Memory)and a semiconductor device, and to a technology effective forapplication to a so-called open bit line type wherein dynamic memorycells are respectively placed at points where word lines and bit linesintersect.

According to investigations subsequent to the completion of the presentinvention, it has been revealed that Japanese Patent ApplicationLaid-Open No. Sho 59(1984)-2365 (hereinafter called “prior art 1”),Japanese Patent Application Laid-Open No. Sho 60(1985)-195795(hereinafter called “prior art 2”), Japanese Patent ApplicationLaid-Open No. Sho 60(1985)-211871 (hereinafter called “prior art 3”),and Japanese Patent Application Laid-Open No. Hei 9(1997)-135009(hereinafter called “prior art 4”) have existed as those considered tobe related to the present invention to be described later.

The prior arts 1 through 3 relate to a technology which makes use ofeven information storage capacitors using MOS capacity and supplies avoltage to each of plate electrodes employed in an open bit line type(one-intersection type or system). In the publication of the prior art1, first wires crossed in a direction orthogonal to each bit line andconnected at plural points, second wires for interconnecting the firstwires with one another, and third wires for connecting central portionsof the second wires to their corresponding power or source lines areprovided to achieve the uniformity of accurate potential distributionsof opposite electrodes of the information storage capacitors. In thepublication of the prior art 2, a resistor is provided between two plateelectrodes provided with a sense amplifier interposed therebetween tothereby delay a change in the potential of each plate electrode inassociation with a change in substrate voltage at,the time thatinformation stored in each memory cell is read out to a bit line. In thepublication of the prior art 3, a plate electrode and wires forsupplying voltages thereto are formed of a metal having a high meltingpoint and low in resistance, or silicide of the metal and silicon.Alternatively, a plurality of metal wiring layers are provided on theplate electrode.

According to the prior art 1, a problem developed due to the fact that asource voltage changed according to the operation of a peripheralcircuit is not transferred to the entirety of a plate electrode, issolved by laying out voltage-supplying power or source wires at pluralpoints of the plate electrode and uniformizing the potential of theplate electrode on the whole according to the change in potential due tothe operation of the peripheral circuit. According to the prior art 2, aproblem developed due to the fact that a relative potential changediffers from a change in potential on the substrate side, is solved byconnecting the two plate electrodes trough a resistor having timeconstant associated with the change in potential on the substrate side.In the prior art 3 on the other hand, the problem that a change inpotential supplied to each plate electrode from its corresponding bitline through a storage capacitor would lead to the application of avoltage to the plate electrode, is solved by reducing the resistance ofeach wire connected to the plate electrode.

SUMMARY OF THE INVENTION

It has been desirable to reduce the cost of a dynamic RAM (hereinaftercalled simply “DRAM”). To this end, a reduction in chip size is mosteffective. A scale-down has heretofore been pushed forward to reduce amemory cell size. It is however necessary to change even an operatingmode or system of a memory array and thereby make a further reduction incell size. By changing the operating mode of the memory array from atwo-intersection type to a one-intersection type, the cell size canideally be reduced to 75% by using the same design rule. However, theone-intersection type memory array has a problem in that array noiseplaced on each bit line or the like is high, as compared with thetwo-intersection type memory array. Thus, a product application becomesdifficult unless it is solved.

Therefore, a discussion has been made of noise developed when the memorycells employed in the conventional two-intersection type are used asthey are to configure the one-intersection type memory array. Thus, ithas been revealed that an unneglible parasitic capacity has existedbetween each bit line and the plate electrode when the memory cell is aCOB (Capacitor over Bit-line) cell, so-called deep hole STC (suchcylinder shape that a lower electrode SN of each capacitor is formed onan inner wall of a hole defined in an interlayer dielectric) except forthe MOS capacity. Even if the techniques described in the prior arts 1to 3 are used as they are to perform the supply of a voltage, it hasbeen found out that the array noise placed on the bit line, could not bereduced.

A description will be made of degradation in operating margin for eachmemory array due to plate noise by reference to FIGS. 16A and 16B. Inthe worst case of a one-intersection memory array shown in FIG. 16A, bitlines in a selected mat are all amplified to a low level (L) except forone bit line according to an amplifying operation of each senseamplifier, and bit lines in a non-selected mat are all amplified to ahigh level (H) except for one bit line. At this time, there is a dangerthat only one bit line in the selected mat, on which a high-level (H)signal appears, is subjected to noise from a plate electrode, wherebythe signal would be amplified erroneously.

Now consider, as one example, where a word line WL0 is activated so thata high-level (H) signal appears on a bit line BL1T alone and a low-level(L) signal is read out onto other bit lines BL0T and BL2T and the like.Further, the high-level (H) signal developed on the bit line BL1T isregarded as small due to the reason such as the leakage or the like ofan electrical charge for holding information in each memory cell. When asense amplifier is activated, such bit lines BL0T/B, BL2T/B, etc. thatsignals greatly appear between complementary bit lines, are amplifiedfast in signal.

On the other hand, a bit line BL1T/B small in signal is slow inamplifying rate. At this time, negative noise is developed in a plateelectrode PL0 of a selected mat from the bit lines BL0T, BL2T, etc.through a parasitic capacity CBLSN and a memory cell capacitor CSbetween storage nodes SN. To the contrary, positive noise is produced ina plate electrode PL1 of a mat adjacent thereto from bit lines BL0B andBL2B, etc. When these noise are returned from the plate electrode PL1 tothe bit line BL1T/B on which a reverse signal appears, through thecapacitor CS and the parasitic capacity CBLSN, a signal amount decreasesso that the bit line is reversed erroneously.

Thus, the open bit line type memory array referred to above gets intogreat danger that information is erroneously read when the amount of asignal charge stored in each memory cell decreases. This leads todegradation in refresh characteristic and can result in a greatreduction in yield of a DRAM. While the above description has been madewith the noise developed in each plate electrode as an example, there isa fear of noise having a similar mechanism being produced even in anon-selected word line WL and a substrate for each memory cell. Thesenoise degrade a read margin for the memory array.

An object of the present invention is to provide an open bit line typedynamic RAM and a semiconductor device capable of improving an operatingmargin. Another object of the present invention is to provide a dynamicRAM and a semiconductor device capable of achieving high integration andthe stabilization of their operations. The above, and other objects andnovel features of the present invention will become apparent from thedescription of the present specification and the accompanying drawings.

A summary of a typical one of the inventions disclosed in the presentapplication will be described briefly as follows: In a dynamic RAMcomprising a plurality of word lines respectively connected to addressselect terminals of a plurality of dynamic memory cells, a plurality ofcomplementary bit line pairs respectively connected to input/outputterminals of the plurality of dynamic memory cells and placed indirections opposite to one another, and a sense amplifier array which issupplied with an operating voltage according to an operation timingsignal and comprises a plurality of latch circuits for respectivelyamplifying the differences in voltage between the complementary bit linepairs, common electrodes provided in opposing relationship to storagenodes corresponding to connecting points between address select MOSFETsand information storage capacitors of the plurality of dynamic memorycells provided on both sides with the sense amplifier array as thecenter are connected to one another while circuit connections in thesense amplifier array are being ensured by wiring means using the commonelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIGS. 1A and 1B are respectively configurational views showing oneembodiment of a dynamic RAM according to the present invention;

FIGS. 2A and 2B are respectively explanatory views illustrating a memorycell of a dynamic RAM according to the present invention;

FIG. 3 is a circuit diagram depicting one embodiment of a senseamplifier unit of the dynamic RAM according to the present invention;

FIG. 4 is a layout diagram of a lower layer showing one embodiment ofthe sense amplifier unit of the dynamic RAM according to the presentinvention;

FIG. 5 is a layout diagram of an upper layer illustrating one embodimentof the sense amplifier unit of the dynamic RAM according to the presentinvention;

FIG. 6 is a partly sectional structural view of FIG. 5;

FIG. 7 is a cross-sectional view showing one embodiment of a sub-worddriver unit of the dynamic RAM according to the present invention;

FIG. 8 is a layout diagram showing another embodiment of a method ofsupplying a voltage to each plate electrode employed in the dynamic RAMaccording to the present invention;

FIGS. 9A and 9B are respectively explanatory views showing oneembodiment of power wires for a word line selection circuit employed inthe dynamic RAM according to the present invention;

FIG. 10 is a cross-sectional view illustrating one embodiment of adynamic memory cell according to the present invention;

FIG. 11 is a layout diagram depicting one embodiment of a method ofwiring a substrate power supply employed in the dynamic RAM according tothe present invention;

FIG. 12 is a cross-sectional view showing other embodiments of thememory cell and the sense amplifier unit employed in the dynamic RAMaccording to the present invention;

FIG. 13 is a circuit diagram illustrating one embodiment of a sub-worddriver employed in the dynamic RAM according to the present invention;

FIG. 14 is a schematic layout diagram depicting one embodiment of adynamic RAM to which the present invention is applied;

FIG. 15 is a block diagram showing one embodiment of a dynamic RAMaccording to the present invention; and

FIGS. 16A and 16B are respectively diagrams for describingone-intersection type memory array discussed by the inventors of thepresent application and noise produced therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

FIG. 14 schematically shows the layout of one embodiment of a dynamicRAM to which the present invention is applied. Of respective circuitblocks constituting the dynamic RAM to which the present invention isapplied, a principal portion related to the invention is shown in thesame drawing as is understood therefrom. It is formed on a singlesemiconductor substrate like monocrystal silicon by the knownmanufacturing technology of semiconductor integrated circuit.

In the present embodiment, memory arrays are divided into four as awhole although not restricted in particular. An address input circuit, adata input/output circuit, an input/output interface circuit comprisinga row of bonding pads, and a power circuit including a step-down and ade-boosting circuit, etc. are provided in central portions 14 with beingdivided into the left and right with respect to the longitudinaldirection of a semiconductor chip. Memory array controllers (AC) 11 andmain word drivers (MWD) 12 are respectively placed in portionscontiguous to the memory arrays located on both sides of these centralportions 14. Each of the memory array controllers 11 comprises a controlcircuit for driving a sub word select line and a sense amplifier, and amain amplifier. In each individual memory arrays comprised of fourdivided into two on both sides and two up and down with respect to thelongitudinal direction of the semiconductor chip as described above,column decoder areas (YDC) 13 are provided in upper and lower centralportions with respect to the longitudinal direction of the semiconductorchip.

In each memory array referred to above, the main word driver area 12forms or produces a signal for selecting a main word line which extendsso as to penetrate one memory array corresponding to it. Sub-word selectline drivers for sub-word selection are also provided in the main worddriver areas 12. As will be described later, each sub-word select linedriver extends in parallel to the main word line and produces a signalfor selecting a sub-word select line. The column decoder 13 forms orproduces a signal for selecting a column select line extended so as topenetrate one memory array corresponding to it.

Each of the memory arrays is divided into a plurality of memory cellarrays (hereinafter called “sub arrays”) 15. Th sub array 15 is formedso as to be surrounded by sense amplifier areas 16 and sub-word driverareas 17 as illustrated by its enlarged view. Portions where the senseamplifier areas 16 and the sub-word driver areas 17 intersectrespectively, are called intersecting areas (cross areas) 18. A senseamplifier provided for the sense amplifier area 16 comprises a latchcircuit having a CMOS configuration and is defined as a so-called oneintersection system or open bit line system which amplifies signals oncomplementary bit lines extended to both sides of each sense amplifierwith the sense amplifier as the center.

Although not restricted in particular, one memory cell array (sub array)15 shown as the enlarged view comprises 512 sub-word lines and ones (ordata lines) of complementary bit lines orthogonal thereto, which areprovided as 1024 lines. Since the sub arrays 15 in each memory arrayreferred to above are provided thirty two for normal purpose in a bitline direction and provided two for reference purpose in the bit linedirection as viewed in a bit-line extending direction. Since the subarrays 15 are provided with one pairs of complementary bit lines withthe sense amplifiers 16 as the centers, the bit lines are substantiallydivided into 16 by the sub arrays 15 as viewed in the bit-line extendingdirections. Further, the sub arrays 15 are provided four in a word-lineextending direction. Thus, the sub-word lines are divided into four bythe sub arrays 15 as viewed in the word-line extending direction.

Since the 1024 bit lines are provided for each sub array 15, memorycells corresponding to about 4K are connected in a word line direction.Since the 512 sub-word lines are provided, memory cells corresponding to512×32=16K are connected in the bit-line direction. Thus, one memoryarray has a storage capacity of 4K×16K=64 Mbits, and the four memoryarrays have a storage capacity of 4×64M=256 Mbits as the whole of amemory chip 10.

In the present application, the term “MOS” is understood as a metaloxide semiconductor configuration originally called for simplicity orbrevity. However, the recent generally-named MOSs include those obtainedby changing a metal of essential portions of a semiconductor device toan electrical conductor such as polysilicon which does not belong to themetal and changing oxide to another insulator. Also CMOSs are nowunderstood as having a wide technical meaning corresponding to a changein how to grasp the MOSs referred to above. MOSFETs are also similarlytaken as the meaning including such a wide construction as substantiallytaken as an insulated-gate field effect transistor without beingunderstood in a narrow sense. CMOSs, MOSFETs, etc. employed in thepresent invention follow general naming and include even transistors.

FIGS. 1A and 1B are respectively configurational views of one embodimentfor describing the dynamic RAM according to the present invention. FIG.1A shows circuits associated with two sub arrays (or memory mats) MAT0and MAT1 provided in the dynamic RAM of the hierarchical word-linesystem, and FIG. 1B shows layouts corresponding thereto. In FIG. 1B,memory cells MCs each comprising MOSFET and a cell capacitor orcapacitance CS are respectively connected to all points where bit linesBL and sub-word lines WL intersect. Each sense amplifier SA is connectedto the bit lines, whereas sub-word drivers SWD are connected to the wordlines WL.

In the present embodiment, the eight sub-word lines are arranged foreach main word line in a complementary bit-line direction to decreasethe number of the main word lines, in other words, reduce the wiringpitch of each main word line as will be described later, although notrestricted in particular. A sub-word selection driver is provided toselect one sub-word line from the sub-word lines divided into four inthe main word-line direction and assigned in the complementary bit-linedirection by eight as shown in FIG. 14. This sub-word selection driverproduces a signal for selecting one from the eight sub-word select lineswhich extend in the direction of an arrangement of the sub-word drivers(sub-word driver arrays SWDA). Although not shown in the drawing, themain word lines MWL are extended in parallel to the sub-word lines WL.Although not shown in the drawing, each column selection line YS isdisposed in parallel to the direction of extension of each bit line BLorthogonal thereto.

The sense amplifiers SA of a sense amplifier array SAA provided betweenthe two sub arrays MAT0 and MAT1 are connected to their correspondingcomplementary bit lines such as to extend to both sides of the two subarrays MAT0 and MAT1. As to these sense amplifiers SA, one senseamplifier SA is arranged every two bit lines in the sense amplifierarray SAA. Thus, the sense amplifier array SAA provided between the twosub arrays MAT0 and MAT1 is provided with 512 sense amplifiers SAcorresponding to half of the 1024 bit lines where the 1024 bit linesexist.

In the sub array MAT0, the remaining 512 bit lines are connected totheir corresponding sense amplifiers SA provided in a sense amplifierarray SAA on the side opposite to the memory mat MAT1. In the sub arrayMAT1, the remaining 512 bit lines are connected to their correspondingsense amplifiers SA provided in a sense amplifier array SAA provided onthe side opposite to the sub array MAT0. Since one sense amplifier maybe formed every two bit lines according to the dispersed placement orlayout of such sense amplifiers SA on both sides as viewed in thebit-line direction, the sub arrays and the sense amplifier arrays can beformed with high density so as to cause the pitches of the senseamplifier SA and the bit line BL to coincide with each other.

This is similar even to the sub-word drivers SWD. 512 sub-word lines WLprovided in the sub array MAT0 are divided 256 by 256, which in turn areconnected to their corresponding 256 sub-word drivers SWD of thesub-word driver arrays SWDA placed on both sides of the sub array MAT0.In the present embodiment, the sub-word drivers SWD provided two by twoare dispersively placed with two sub-word lines WL as each pair. Namely,two sub-word drivers are placed on the one-end side (on the upper sidein the drawing) of the sub array MAT0 with the sub-word linescorresponding to two memory cells which share the use of a portionconnected to each bit line, as one pair, whereas two sub-word driversare placed on the other end side (on the lower side in the drawing) ofthe sub array MAT0 with the similar two sub-word lines adjacent theretoas one pair.

Although not shown in the drawing, the sub-word drivers SWD form orproduce signals for selecting sub-word lines for sub arrays provided onboth sides with the sub-word driver array SWDA in which the sub-worddrivers are formed, interposed therebetween. Thus, the sub-word driversSWD can be dispersively placed with satisfactory efficiency inassociation with the sub-word lines each formed so as to coincide withan array pitch of each memory cell, and the operation of selecting eachsub-word line WL can be carried out at high speed.

The memory cells MC are respectively formed at points where the bitlines BL and sub-word lines WL included in the memory arrays (or memorymats) MAT0 and MAT1 or the like surrounded by the sub-word driver arraysSWDA and sense amplifier arrays SAA. In the sub array MAT0 with thememory cells MC formed therein, upper electrodes (plate electrodes) PLof storage capacitors CS are formed in common between all the memorycells MC in the sub arrays MAT0 and MAT1 as plane electrodes as shown inFIG. 1B. The supply of power to the plate electrodes PL is carried outat the boundary between the sub-word driver array SWDA and each of thesub arrays MAT0 and MAT1 through a connecting portion PLCT from a powerwire VPLT wired in the direction of extension of each bit line BL. Inthe same drawing, storage nodes SN are respectively lower electrodes ofthe storage capacitors CS and indicate portions for connection toaddress selection MOSFETs.

In the present embodiment, the plate electrodes PL0 and PL1 respectivelyformed in the sub arrays MAT0 and MAT1 provided on both sides of eachsense amplifier array SAA are connected to one another by wires PLSAusing a plate layer itself. Further, the wires PLSA are provided inplural form so as to penetrate the sense amplifier arrays SAA, therebygreatly reducing resistance between the two plate electrodes PL0 andPL1. Thus, phase-reversal noise developed in the plate electrodes PL0and PL1 when a small signal read from each memory cell MC selectedbetween complementary bit lines BL for the sub arrays MAT0 and MAT1 isamplified by the corresponding sense amplifier SA, can be cancelled outat high speed, thereby making it possible to greatly reduce the noiseproduced in the plate electrodes PL0 and PL1.

Since the noise returned to the bit line BL through the parasiticcapacitor CBLSN or the like between each of the plate electrodes PL0 andPL1 and each bit line BL described in FIG. 16 is reduced owing to thereduction in the noise developed in the plate electrodes PL0 and PL1upon the above amplifying operation of the sense amplifier SA, the senseamplifier SA is capable of sensing even a smaller signal. Namely, it ispossible to greatly enlarge an operation margin for eachone-intersection DRAM array.

A diagram for describing one embodiment of a memory cell employed in adynamic RAM according to the present invention is shown in FIG. 2. FIG.2A shows the layout of memory cell arrays in two sub arrays MAT0 andMAT1, and FIG. 2B shows an element or device sectional structure of aportion taken along line A-A′ of FIG. 2A, respectively. In the samedrawings, the layout and cross-section of a sense amplifier SA areaprovided between the MAT0 and MAT1 are omitted.

ACT indicates an active region of each MOSFET, SNCT indicates a contact(connecting portion) for connecting a storage node SN of each memorycell and source and drain diffusion layers corresponding to the storagenode SN, of the MOSFET formed in the active region ACT to each other,and BLCT indicates a contact (connecting portion) for connecting thecorresponding bit line BL and source and drain diffusion layers,corresponding to an input/output terminal of each memory cellcorresponding to the bit line BL, of the MOSFET formed in the activeregion ACT to each other. CP indicates a capacitance insulating film ofa storage capacitor. Here, a metal layer M1 corresponding to a firstlayer, and each bit line BL comprises the same wiring layer. Further, apolysilicon layer FG corresponding to a first layer, and each sub-wordline WL are also comprised of the same wiring layer.

As shown in FIG. 2B, plate electrodes PL for the sub arrays MAT0 andMAT1 provided on both sides of the SA are connected using electrodesthemselves constituting the plate electrodes PL without turning off themon the sense amplifier SA, whereby the resistance between the plateelectrode PL of the sub array MAT0 and the plate electrode PL of the subarray MAT1 can greatly be reduced. The memory cell makes use of a COB(capacitor over Bitline) structure. Namely, the storage nodes SN areprovided over the bit lines BL. Thus, since the plate electrodes PL canbe formed in one flat form without being cut by the bit lines BL and theconnecting portions BLCT of the address selection MOSFETs within the subarrays MATs, the resistance between the plate electrodes PL can bereduced.

Since the bit line BL exists on the plate electrode PL when a CUB(Capacitor under Bitline) structure is adopted contrary to the presentembodiment, it is necessary to define holes in the plate electrodes PLwithin each sub array MAT and bring such connecting portions BLCT to theactive regions ACT for purpose of connecting each bit line BL and thesource and drain of the address selection MOSFET. Therefore, the valueof the resistance of the PL increases.

The present embodiment has an advantage in that as shown in FIG. 2B, theplate electrode PL takes a laminated structure using PL(D) and PL(U),and the sheet resistance value of such plate electrode PL can belowered. Now consider where a high dielectric film such as BST or Ta₂O₅is used for the capacitive insulating film CP of the storage capacitoras one example. When Ru is used for the lower electrode (storage node)SN and upper-electrode lower layer PL(D) in this case, the capacity ofthe storage capacitor CS can be increased. Since Ru is low in sheetresistance value as compared with the conventionally used poly Si, theresistance value of each plate electrode PL can be reduced.

Further, if W is stacked on this structure as the plate electrode PL(U),then the resistance value of each plate electrode PL can further bereduced. When the resistance value of the plate electrode itself isreduced in this way, the speed of canceling out noise lying on the plateelectrodes PL is made fast and hence the noise developed in the plateelectrodes PL can be reduced. Further, TiN may be used as the plateelectrode PL(D). Even in this case, an advantageous effect similar tothe above can be obtained.

In the above-described structure of memory cell as is apparent from thelayout of FIG. 2A, the connecting portion SNCT for connecting eachstorage node SN and the source and drain diffusion layers of each MOSFETis provided adjacent to each of the bit lines BL. Namely, the parasiticcapacity exists between the storage node of the memory cell and the bitline BL as viewed in the vertical direction of a cross-section of thestructure. Since the parasitic capacity constitutes the parasiticcapacitance CBLSN shown in FIG. 16, the interconnection of the plateelectrodes employed in the present invention by the wires usingthemselves becomes useful.

FIG. 3 is a circuit diagram showing one embodiment of a sense amplifierunit of the dynamic RAM according to the present invention. A senseamplifier SA comprises a CMOS latch circuit comprising N channelamplifying MOSFETs Q5 and Q6 and P channel amplifying MOSFETs Q7 and Q8whose gates and drains are cross-connected and brought to latch form.The sources of the N channel MOSFETs Q5 and Q6 are electricallyconnected to a common source line CSN. The sources of the P channelMOSFETs Q7 and Q8 are electrically connected to a common source lineCSP.

Power switches MOSFETs Q3 and Q4 are respectively electrically connectedto the common source lines CSN and CSP. Although not restricted inparticular, a ground potential supply line VSSA is given or offered tothe common source line CSN to which the sources of the N channelamplifying MOSFETs Q5 and Q6 are electrically connected, by the Nchannel power switch MOSFET Q3 dispersively laid out in such a senseamplifier area. The common source line CSP to which the sources of the Pchannel amplifying MOSFETs Q7 and Q8 are electrically connected, isprovided with the N channel power MOSFET Q4 to supply an operatingvoltage VDD thereto.

The gates of the N channel power MOSFETs Q3 and Q4 are supplied with asense amplifier activation signal SAN. Although not restricted inparticular, the high level of the SAN is defined as a signal having aboosted voltage VPP level. Namely, the boosted voltage VPP is oneboosted to greater than or equal to a threshold voltage of the MOSFET Q4with respect to a source voltage VDD. This voltage VPP sufficientlybrings the N channel MOSFET Q4 to an ON state, thereby making itpossible to set the potential of the common source line CSP to thesource voltage VDD.

A precharge (equalize) circuit comprising an equalize MOSFET Q11 forshort-circuiting complementary bit lines BL0T and BL0B, and switchMOSFETs Q9 and Q10 for respectively supplying a half precharge voltageVBLR to the complementary bit lines BL0T and BL0B is provided atinput/output nodes of the sense amplifier SA. The gates of these MOSFETsQ9 through Q11 are supplied with a precharge (bit-line equalize) signalBLEQ in common. As to a driver circuit for forming or producing theprecharge signal BLEQ, although not shown in the drawing, an invertercircuit is provided in each cross area 18 shown in FIG. 14 to make therising edge and falling edge of the precharge signal BLEQ fast. Namely,the driver circuit is one which performs, at high speed, switchingbetween the MOSFETs Q9 through Q11 constituting the precharge circuitthrough the inverter circuits dispersively provided in each individualcross areas 18, prior to word-line selecting timing upon commencement ofa memory access.

The pair of input/output nodes of the sense amplifier SA is electricallyconnected to local (sub) input/output lines SIO, SIO0T and SIO0Bextended along a sense amplifier array through a column (Y) switchcircuit comprising MOSFETs Q2 and Q3 as well as to the complementary bitlines BL0T and BL0B. The gates of the MOSFETs Q1 and Q2 are electricallyconnected to a column selection line YS. When the present columnselection line YS is brought to a selection level (high level), they areturned ON to electrically connect the input/output nodes of the senseamplifier SA and the local input/output lines SIO0T and SIO0B to oneanother. Adjacent bit lines are also electrically connected to localinput/output lines SIO1T and SIO1B through a switch circuit similar tothe above, which is switch-controlled by the same column selection lineYS.

Thus, the input/output nodes of the sense amplifier SA amplify a smallvoltage change with respect to a half precharge voltage on each bitline, which changes according to an electrical charge stored in eachmemory cell electrically connected to a point intersecting a word lineof a sub array selected from two sub arrays (e.g., MAT0 and MAT1)provided with the input/output nodes interposed therebetween while ahalf precharge voltage on each bit line on the non-selected sub arrayside is being used as a reference voltage. One selected by the columnselection line YS is transferred to the local input/output lines SIO0Tand SIO0B, and SIO1T and SIO1B through the column switch circuit (Q1 andQ2).

As shown in FIG. 14, the local input/output lines SIO0T and SIO0B, andSIO1T and SIO1B extend over the sense amplifier arrays aligned along theextension direction of the main word lines. Signals amplified throughsub amplifier circuits are transferred to main amplifiers provided inmain word driver MWD units through main input/output lines each extendedin the direction identical thereto. In one memory array obtained bydividing the memory chip into four on the memory chip, for example, thesignals are outputted in parallel in 16-bit units according to thenumber of divisions of the sub array. The memory arrays divided intofour respectively constitute memory banks as will be described later.

A layout of one embodiment of the sense amplifier SA shown in FIG. 3 isshown in FIGS. 4 and 5. FIG. 4 shows the layout of contact units TC1connected to metal layers Ml and M2 corresponding to first and secondlayers respectively, and layers below the metal layer M1, whereas FIG. 5shows the layout of layers above the contact unit TC1. In FIGS. 3through 5, CCP correspond to cross-coupled P channel MOSFETs (Q7 andQ8), CSD corresponds to a common source driver (Q3 and Q4), CCNcorrespond to cross-coupled N channel MOSFETs (Q5 and Q6), PCcorresponds to a precharge circuit (Q9 through Q11), and YG correspondsto a Y gate circuit (Q1 and Q2), respectively. They correspond to thoseshown in FIGS. 3 through 5.

Sectional structures of portions indicated by a and b in FIG. 5 areshown in FIG. 6. ACT indicates an active region of each MOSFET, i.e., adevice or element forming region in which a source, a drain and achannel portion are formed, FG (polysilicon corresponding to a firstlayer) indicates a gate electrode of each MOSFET and a sub-word line,M1, M2 and M3 respectively indicate metal wiring layers corresponding tofirst, second and third layers, CONT indicates a contact for connectingthe M1 and FG or the M1 and ACT, TC1 indicates a contact for connectingthe M2 and M1, and TC2 indicates a contact for connecting the M3 and M2,respectively.

As shown in FIG. 5, the plate electrode PL is wired from the metalwiring layer M2 corresponding to the second layer above the plateelectrode PL so as to avoid an area through which the contact TC1corresponding to a layer below the plate electrode PL passes. The plateelectrodes PL0 and PL1 of the sub arrays MAT0 and MAT1 are connected toone another by wires comprising the same conductor layer as the plateelectrodes PL0 and PL1. The PL wires can be provided within the SAA inplural form in the proportions of about one to the pitch equivalent tothe four bit lines BL. Incidentally, since many lines equivalent to 256as the number of the PL wires are arranged in parallel where one subarray comprises 1024 bit lines, the resistance value of a wire orinterconnection for connecting the two plate electrodes provided withthe sense amplifier array SAA interposed therebetween can be reduced. Itis therefore possible to cancel out complementary noise developed inboth plate electrodes PL1 and PL2 and greatly reduce the noise.

In the present embodiment, each storage node SN is formed in the form ofa deep hole STC structure as shown in FIG. 2B. Namely, the storage nodeSN is formed on an inner wall of a hole defined in an interlayerdielectric and shaped in cylinder form. While the plate electrode PLfalls into the cylinder-shaped storage node SN inside the storage nodeSN if done in this way, the plate electrode PL becomes identical to anupper portion of the storage node SN in height outside the storage nodeSN. Thus, since an upper portion of the plate electrode PL is flattened,it is easy to process the plate electrode PL. Accordingly, an advantageis brought about in that processing (patterning) the plate electrode PLso as to avoid the contact TC1 within the sense amplifier array SAA asdescribed above becomes easy. Namely, a wiring portion for connectingbetween both plate electrodes PL0 and PL1 is formed broader in width andhence the resistance value thereof can be reduced.

FIG. 7 is a cross-sectional view of one embodiment of a sub-word driverSWD. The supply of power to the plate electrode PL is carried out at theboundary between a sub-word driver array SWDA and a sub array MAT0.Since each of plate power lines VPLT wired in a bit-line BL direction iswired by a metal wiring layer M3 corresponding to a third layer, theplate power line is brought to a metal wiring layer M2 corresponding toa second layer with a contact TC2 interposed therebetween. Further, theplate power line is connected to the plate electrode PL through acontact PLCT. Incidentally, the sub-word driver SWD will be explainedlater with reference to FIG. 13.

FIG. 8 shows the layout of another embodiment of a method of supplying avoltage to each plate electrode. In the present embodiment, wires areformed with the same electrode material as the pair of plate electrodesPL0 an PL1 to thereby interconnect the pair of plate electrodes PL0 andPL1 formed with the sense amplifier array SAA interposed therebetween,and the method of supplying the power to each plate electrode isupgraded in addition to the interconnection. The mesh wiring technologypreviously developed by the applicant of the present application is usedfor this type of power supplying method. Since the mesh wiringtechnology has been described in Japanese Patent Application Laid-OpenNo. Hei 9(1997)-135006, it is noted that a reference is made to the meshwiring technology.

In FIG. 8, a wiring layer M3 of the same layer as column selection linesYS is used to place wires on sub-word driver arrays SWDA and sub arrays(MATs). A wiring layer M2 of the same layer as main word lines MWL isused in the transverse direction shown in each drawing orthogonal to thearray selection lines YS to thereby place wires on the sub arrays inparallel thereto. On the sub arrays (MATs), these vertically andhorizontally-extending wires are connected to one another by contactsTC2, thereby making it possible to reduce the resistance value of apower supply line VPLT. Further, since the value of resistance betweenplate electrodes PL0 and PL1 can further be reduced in addition tointerconnecting portions PLSA using the above-described electrodematerial owing to the adoption of such a power supply wiring system,plate-electrode PL noise can be reduced.

FIGS. 9A and 9B are respectively explanatory views showing oneembodiment illustrative of power wires for a word line selection circuitemployed in the dynamic RAM according to the present invention. FIG. 9Ashows circuits corresponding to the two sub arrays MAT0 and MAT1provided in the dynamic RAM of the hierarchical word line system such asshown in FIG. 14, and FIG. 9B shows layouts corresponding thereto,respectively. An advantageous effect can be obtained in that while onlysource or power VSSWL for setting sub-word lines WL to a non-selectionlevel are shown in the drawings, a similar power wiring resistance canbe reduced if each power line for supplying a boosted voltage VPP forsetting each of the sub-word lines WL to a selection level is alsosimilarly wired.

A wiring layer M3 corresponding to the same layer as column selectionlines YS is used in the transverse direction in the drawings to placewires on sub-word driver arrays SWDA and sub arrays (MATs). A wiringlayer M2 of the same layer as main word lines MWL is used in thelongitudinal direction in each drawing to thereby place wires on the subarrays. On the sub arrays, these vertically and horizontally-extendingwires are connected to one another by contacts TC2, whereby theresistance value of the power supply line VSSWL can be reduced. Further,the value of resistance between a sub-word driver SWD power supply ofthe sub array MAT0 and a sub-word driver SWD power supply of the subarray MAT1 can be reduced owing to the adoption of such a wiring system.Thus, noise developed in the sub-word line WL upon sensing each bit lineBL can be reduced, whereby an operating margin for a one-intersectionDRAM array can greatly be enlarged in a manner similar to the embodimentshown in FIG. 1, for example.

FIG. 10 is a cross-sectional view of one embodiment of a dynamic memorycell according to the present invention. In the present embodiment, theresistance value of each sub-word line is lowered with the sub-wordlines as a laminated structure. As one example, a sub-word line WL (D)corresponding to a lower layer is comprised of poly Si, and tungstenhaving a low resistance can be used for a sub-word line WL (U)corresponding to an upper layer. Thus, since noise developed in eachsub-word line WL is canceled out at high speed when the resistance valueof the sub-word line is reduced, sub-word line WL noise is reduced.Alternatively, word lines may be configured by the word lines havingsuch a laminated structure as described above in addition to ahierarchical structure comprising main word lines and sub-word lines.Further, the word lines may be ones to which memory cells correspondingto the four sub arrays are connected. Even in this case, a similaradvantageous effect can be obtained in that the resistance value of eachword line is lowered to thereby reduce noise placed thereon.

FIG. 11 shows the layout of one embodiment of a method of wiring asubstrate source or power supply employed in the dynamic RAM accordingto the present invention. The supply of a substrate power supply VBB toa substrate PWEL with memory cells formed thereon is carried out at theboundary between each of sense amplifier arrays SAA and itscorresponding sub array MAT. FIG. 12 is a cross-sectional view showing aboundary region between a sub array MAT0 and a sub array MAT1. Since aPWEL power supply line VBB wired in the direction of extension of eachword line WL is wired with a metal wiring layer M2 corresponding to asecond layer, the PWEL power supply line VBB is temporarily brought downto a metal wiring layer M1 corresponding to a first layer through eachcontact TC1, followed by connection to a P type well PWEL through acontact CONT.

An N-type well NWEL for forming P channel MOSFETs Q7 and Q8, etc. existsin the sense amplifier array SAA. Therefore, when a deep MNWL (DWEL) isplaced below the sense amplifier SA and each sub array MAT by using atriple well structure, a P-type well region PWEL used as the substratefor each memory cell is separated on both sides of the sense amplifierarray SAA. Thus, when contact with the P-type well region PWEL is doneon both sides of the N-type well region NWEL within one sense amplifierarray SAA, substrate noise can be reduced.

As to wiring for the substrate bias voltage VBB, a wiring layer M3corresponding to the same layer as column selection lines YS is used inthe longitudinal direction in FIG. 11 to place wires on each sub-worddriver array SWDA and sub array MAT. A wiring layer M2 corresponding tothe same layer as main word lines MWL is used in the longitudinaldirection to thereby place wires on the sense amplifier array SAA andthe sub arrays. On the sub arrays, these vertically andhorizontally-extending wires are connected to one another by contactsTC2, whereby the resistance value of a power supply line for supplyingthe substrate bias voltage VBB can be reduced. Further, the resistancebetween P-type well regions PWEL0 and PWEL1 corresponding to the subarrays MAT0 and MAT1 can be reduced owing to the adoption of such awiring system. According to the present embodiment, noise developed inthe substrate when the potential on each bit line BL is amplifiedaccording to the amplifying operation of the sense amplifier SA, can becanceled out at high speed and reduced, whereby an operating margin fora one-intersection DRAM array can greatly be enlarged in a mannersimilar to the embodiment shown in FIG. 1.

FIG. 12 is a cross-sectional view of other embodiments of the memorycell and the sense amplifier unit employed in the dynamic RAM accordingto the present invention. In the cross-sectional view of the memorycell, the resistance of PWEL is reduced with the substrate PWEL for thememory cell as a laminated structure. As one example, a region PWELU fordetermining the operation of a memory cell MOSFET corresponding to anupper layer is defined as Si doped in low concentrations. A PWELDcorresponding to a lower layer is defined as Si doped in highconcentrations for a reduction in resistance. Since noise produced inthe substrate is canceled out at high speed when the resistance of thesubstrate is lowered in this way, substrate noise is reduced.

FIG. 13 is a circuit diagram of one embodiment of a sub-word driveremployed in the dynamic RAM according to the present invention. In thepresent embodiment, one main word line MWL is provided with respect toeight sub word lines WL0 through WL7. Sub-word selection lines FX0through FX7 and FX0B through FX7B are required to select one sub-wordline from the eight sub-word lines. In the present embodiment, bit linesprovided in one sub array are selected half by half by sub-word driverarrays SWDA provided on both sides thereof. Therefore, eight sub-wordselection lines FX1, 2, 5 and 6 and FX1B, 2B, 5B and 6B for selectingthe four sub-word lines corresponding to the half of the eight sub-wordlines are extended over one sub-word driver array shown in the samedrawing.

Eight sub-word selection lines FX0, 3, 4 and 7 and FX0B, 3B, 4B and 7Bfor selecting the four sub-word lines corresponding to the remaininghalf of the eight sub-word lines are extended over sub-word driverarrays provided on the opposite side with the unillustrated sub arrayinterposed therebetween. Sub-word drivers corresponding to sub-wordlines WL1 and WL2, WL2 and WL4, and WL5 and WL6 set with the two as eachpair are alternately provided. Further, a sub-word line WL0 and a groupsub-word line WL7 (different in main word line) adjacent thereto are setas one pair and two sub-word drivers are provided therefor.

One sub-word driver SWD1 comprises a CMOS inverter circuit comprising anN channel MOSFET Q12 and a P channel MOSFET Q13, and an N channel MOSFETQ14 provided in parallel to the N channel MOSFET Q12. The sources of theN channel MOSFETs Q12 and 14 are respectively electrically connected toa power supply line VSSWL corresponding to a non-selection level VSS(0V) of a sub-word line. A power supply line VPP for supplying a boostedvoltage is provided in an N well region in which the P channel MOSFETQ13 is formed. These power supply lines make use of such amesh-structured wire as in the embodiment referred to above.

The gates of the MOSFETs Q12 and Q13 constituting the CMOS invertercircuit of the sub-word driver SWD1 are electrically connected to theircorresponding main word line MWL in common with the gates of similarMOSFETs in the remaining three sub-word drivers. The sources of the Pchannel MOSFETs Q13 constituting the four CMOS inverter circuits areelectrically connected to their corresponding sub-word selection lineFX1. The sub-word selection line FX1B is provided for the gate of theMOSFET Q14 provided in the sub-word driver SWD1. The sub-word selectionlines FX2 and FX2B, FX5 and FX5B, and FX6 and FX6B are respectivelyelectrically connected to the remaining three sub-word drivers SWD2,SWD5 and SWD6.

When the sub-word line WL1 is selected, the main word line MWL isbrought to a low level. Further, the sub-word selection line FX1corresponding to the sub-word line WL1 is brought to a high level like aboosted voltage VPP. Thus, the P channel MOSFET Q13 of the sub-worddriver SWD1 is turned on to transfer the selection level VPP on thesub-word selection line FX1 to the sub-word line WL1. At this time, theMOSFET Q14 is kept in an off state in response to a low level of thesub-word selection line FX1B in the sub-word driver SWD1.

In other sub-word drivers SWD2, SWD5 and SWD6 in which the main wordline MWL is brought to a selected state corresponding to a low level,the P channel MOSFETs are turned on. However, the N channel MOSFETs areturned on according to high levels of the sub-word selection lines FX2B,FX5B and FX6B to bring the sub-word lines WL2, WL5 and WL6 to thenon-selection level VSS. In the non-selected sub-word drivers in whichthe main word line MWL is brought to the high level, the N channelMOSFETs of the CMOS inverter circuits are turned on by the high level ofthe main word line MWL to thereby bring each individual sub-word linesto the non-selection level VSS.

Since the pair of sub-word lines corresponding to the two sub arrays isselected by the three MOSFETs in this way, sub-word drivers can beformed so as to coincide with the pitches of the sub-word lines WLprovided in the memory array (sub-array) of the open bit line system andplaced in high concentrations. Sub-word drivers can be laid out whichare adapted to one-intersection or open bit line system capable ofideally reducing each cell size to 75% by using the same design rule asone for a two-intersection system.

When the sub-word drivers are dispersively laid out on both sides ofeach sub array MAT according to two-by-two combinations every twosub-word lines WL as described above, the P channel MOSFETs constitutingthe two sub-word drivers can be formed in the same N type well region,and the N channel MOSFETs can be formed in the same P type well region.As a result, the sub-word drivers can be brought into high integration.This is similar even to the above-described sense amplifiers, which aredispersively placed on both sides of each sub array MAT according totwo-by-two combinations every two bit lines BL.

FIG. 15 is a block diagram showing one embodiment of a dynamic RAMaccording to the present invention. The dynamic RAM showing the presentembodiment is intended for a DDR SDRAM (Double Data Rate SynchronousDynamic Random Access Memory; hereinafter called simply “DDR SDRAM”).Although not restricted in particular, the DDR SDRAM according to thepresent embodiment is provided with four memory arrays 200A through 200Din association with four memory banks. The memory arrays 200A through200D respectively associated with the four memory banks 0 through 3 areequipped with dynamic memory cells placed in matrix form. According tothe drawing, selection terminals of memory cells placed in the samecolumn are connected to their corresponding word lines (not shown) setevery columns, and data input/output terminals of memory cells placed inthe same row are connected to complementary data lines (not shown) setevery rows.

One of unillustrated word lines in the memory array 200A is driven to aselection level according to the result of decoding of each row addresssignal by a row decoder (Row DEC) 201A. Unillustrated complementary datalines in the memory array 200A are coupled to their corresponding I/Olines of a sense amplifier (Sense AMP) 202A and a column selectioncircuit (Column Dec) 203A. The sense amplifier 202A is a circuit fordetecting small potential differences which appear on the respectivecomplementary data lines according to the reading of data from memorycells and amplifying the same. The column selection circuit 203Aprovided for the sense amplifier 202A includes a switch circuit forselecting the complementary data lines separately and bringing theselected ones and complementary I/O lines into conduction. The columnswitch circuit is selectively operated according to the result ofdecoding of each column address signal by the column decoder 203A.

The memory arrays 200B through 200D are also similarly provided with rowdecoders 201B through 201D, sense amplifiers 203B through 203D andcolumn selection circuits 203B through 203D respectively. Thecomplementary I/O lines are shared among the respective memory banks andconnected to an output terminal of a data input/output circuit (DinBuffer) 210 having a write buffer and an input terminal of a data outputcircuit (Dout Buffer) 211 including a main amplifier. Although notrestricted in particular, a terminal DQ serves as a data input/outputterminal for inputting or outputting data D0 through D15 comprising 16bits. A DQS buffer (DQS buffer) 215 forms or produces a data strobesignal for data outputted from the terminal DQ upon a read operation.

Address signals A0 through A14 supplied from an address input terminalare temporarily stored in an address buffer (Address Buffer) 204. Of theaddress signals inputted in time sequence, row address signals arestored in a row address buffer (Row Address Buffer) 205, and columnaddress signals are stored in a column address buffer (Column AddressBuffer) 206. A refresh counter (Refresh Counter) 208 generates rowaddresses at automatic refresh (Automatic Refresh) and self refresh(Self Refresh).

In the case of a storage capacity of 256 Mbits, for example, an addressterminal for inputting the address signal A14 as the column addresssignal is provided when a memory access is carried out in 2-bit units.In an ×4-bit configuration, the address signals up to the address signalA11 are rendered valid. In an ×8-bit configuration, the address signalsup to the address signal A10 are made valid, and the address signals upto the address signal A9 are rendered valid in an ×16-bit configuration.In the case of a storage capacity of 64 Mbits, the address signals up tothe address signal A10 are rendered valid in an ×4-bit configuration,and the address signals up to the address signal A9 are made valid in an×8-bit configuration. Further, the address signals up to the addresssignal A8 are set valid in an ×16-bit configuration as shown in thedrawing.

The output of the column address buffer 206 is supplied to a columnaddress counter (Column Address Counter) 207 as preset data therefor.The column address counter 207 outputs column address signals defined asthe preset data or values obtained by sequentially incrementing thecolumn address signals to the column address decoders 203A through 203Din a burst mode specified by a command or the like to be describedlater.

A mode register(Mode Register) 213 holds various operation modeinformation therein. Of the row decoders (Row Decoders) 201A through201D, only one corresponding to the bank specified by a bank select(Bank Select) circuit 212 is activated to allow the operation ofselecting a word line. Although not restricted in particular, a controlcircuit (Control Logic) 209 is supplied with external control signalssuch as clock signals CLK, /CLK (symbol / means that signals markedtherewith are row enable signals), a clock enable signal CKE, a chipselect signal /CS, a column address strobe signal /CAS, a row addressstrobe signal /RAS and a write enable signal /WE, etc., /DM and DQS, andaddress signals inputted through the mode register 213. The controlcircuit 209 forms internal timing signals for controlling an operationmode for the DDR SDRAM and the operations of the circuit blocks, basedon changes in the levels of these signals, timing, etc. and is providedwith input buffers respectively corresponding to the signals.

The clock signals CLK and /CLK are inputted to a DLL circuit 214 througha clock buffer, from which an internal clock is generated. Although notrestricted in particular, the internal clock is used as a signal to beinputted to each of the data output circuit 211 and the DQS buffer 215.The clock signals sent via the clock buffer are supplied to clockterminals used for the supply to the data input circuit 210 and thecolumn address counter 207.

Other external input signals are rendered significant in synchronismwith the rising edge of the internal clock signal. The chip selectsignal /CS provides instructions for the commencement of a command inputcycle according to its low level. When the chip select signal /CS is ofa high level (kept in a chip non-selected state), other inputs do notmake sense. However, the state of selection of each memory bank, and itsinternal operations such as a burst operation, etc. to be describedlater are not affected by a change to the chip non-selected state. Therespective signals /RAS, /CAS and /WE are different in function fromcorresponding signals employed in the normal DRAM and are set assignificant signals upon defining command cycles to be described later.

The clock enable signal CKE is a signal for indicating the effectivenessof the next clock signal. If the signal CKE is of a high level, then therising edge of the next clock signal CLK is regarded as valid. If thesignal CKE is of a low level, it is then rendered invalid. Incidentally,when an external control signal /OE for performing output enable controlon the data output circuit 211 in a read mode is provided, such a signal/OE is also supplied to the control circuit 209. When the signal is highin level, for example, the data output circuit 211 is brought to ahigh-output impedance state.

The row address signals are defined based on the levels of A0 throughA11 in a row address strobe/bank active command cycle to be describedlater synchronized with the rising edge of the clock signal CLK(internal clock signal).

The address signals A12 and A13 are regarded as bank select signals inthe row address strobe/bank active command cycle. Namely, one of thefour memory banks 0 through 3 is selected according to a combination ofA12 and A13. Although not restricted in particular, the selectioncontrol on the memory banks can be carried out according to processessuch as the activation of only a row decoder on the selected memory bankside, the non-selection of all the column switch circuits on thenon-selected memory bank side, connections to the data input circuit 210and the data output circuit 211 on only the selected memory bank side,etc.

When the ×16-bit configuration is set in 256 Mbits as described above,the column address signals are defined according to the levels of A0through A9 in a read or write command (corresponding to a columnaddress/read command or a column address/write command to be describedlater) cycle synchronized with the rising edge of the clock signal CLK(internal clock). Each of the column addresses defined in this way isset as a start address for a burst access.

Main operation modes of the SDRAM, which are instructed by commands,will next be explained.

(1) Mode Register Set Command (Mo):

This is a command for setting the mode register 30. The correspondingcommand is specified by /CS, /RAS, /CAS and /WE=low level. Data(register set data) to be set is supplied through each of A0 throughA11. Although not restricted in particular, the register set dataincludes a burst length, a CAS latency, a write mode, etc. Although notrestricted in particular, a settable burst length takes 2, 4 and 8 and asettable CAS latency assumes 2 and 2.5. A settable write mode is definedas burst write and single write.

The CAS latency indicates what cycles of internal clock signal arewasted from the falling edge of the /CAS to the output operation of theoutput buffer 211 upon a read operation specified by a columnaddress/read command to be described later. Since an internal operationtime used for the reading of data is required until the read data isestablished or determined, the CAS latency is used to set the internaloperation time according to the use frequency of the internal clocksignal. In other words, when an internal clock signal of a highfrequency is used, the CAS latency is set to a relatively large value.On the other hand, when an internal clock signal of a low frequency isused, the CAS latency is set to a relatively small value.

(2) Row Address Strobe/Bank Active Command (Ac):

This is a command for providing instructions for a row address strobeand making the selection of memory banks based on A12 and A13 effective.This command is specified according to /CS and /RAS=low level and /CASand /WE=high level. At this time, addresses supplied to A0 through A9are taken in or captured as row address signals, whereas signalssupplied to A12 and A13 are captured as signals for selecting the memorybanks. Their capture operations are executed in synchronism with therising edge of the internal clock signal as described above. When thecorresponding command is specified, for example, a word line in a memorybank specified by the command is selected. Thus, memory cells connectedto the corresponding word line and their corresponding complementary bitlines are brought into conduction.

(3) Column Address/Read Command (Re):

This is a command required to start a burst read operation. Further,this is also a command for providing instructions for a column addressstrobe. The present command is specified according to /CS and /CAS=lowlevel and /RAS and /WE=high level. Column addresses supplied to A0through A9 (in the case of the ×16-bit configuration) at this time arecaptured as column address signals respectively. Thus, the capturedcolumn address signals are supplied to the column address counter 207 asburst start addresses.

Before the burst read operation specified thereby, a memory bank and aword line lying therein have been selected in the row addressstrobe/bank active command cycle. Upon the burst read operation in thisstate, memory cells connected to the selected word line are successivelyselected in accordance with each address signal outputted from thecolumn address counter 207 in synchronism with the internal clock signaland items of data are sequentially read therefrom. The number of thesequentially-read data is set as a number specified by the above burstlength. The output buffer 211 starts reading data while waiting for thenumber of cycles in the internal clock signal defined by the CASlatency.

(4) Column Address/Write Command (Wr):

The corresponding command is specified according to /CS, /CAS and/WE=low level and /RAS=high level. Addresses supplied to A0 through A9at this time are captured as column address signals. Thus, the capturedcolumn address signals are supplied to the column address counter 207 asburst start addresses upon the burst write. The procedure of the burstwrite operation specified thereby is also performed in a manner similarto the burst read operation. However, no CAS latency is provided for thewrite operation and the capturing of the write data is started fromafter one clock of the column address/write command cycle.

(5) Precharge Command (Pr):

This is defined as a command for starting a precharge operation on eachmemory bank selected by A12 and A13. This command is specified by /CS,/RAS and /WE=low level and /CAS=high level.

(6) Autorefresh Command:

This is a command required to start autorefresh and specified by /CS,/RAS and /CAS=low level and /WE and CKE=high level.

(7) No-Operation Command (Nop):

This is a command for indicating the non-execution of a substantialoperation and specified by /CS=low level and /RAS, /CAS and /WE=highlevel.

When another memory bank is specified in the course of the burstoperation and the row address strobe/bank active command is suppliedwhile the burst operation is being performed by one memory bank in theDDR SDRAM, no influence is exerted on the operation of one memory bankbeing under the corresponding execution, and the operation of a rowaddress system in another memory bank is allowed.

Thus, unless D0 through D15 collide with one another at a datainput/output terminal comprising 16 bits, for example, the prechargecommand and the row address strobe/bank active command for a memory bankdifferent from a memory bank to be processed or handled by an unfinishedcommand are issued during the execution of the corresponding command tothereby allow the commencement of an internal operation in advance.Since the DDR SDRAM according to the present embodiment performs thememory access in 16-bit units, has the addresses corresponding to about4M, based on the addresses of A0 through A11, and comprises the fourmemory banks as described above, it has a storage capacity of about 256Mbits (4M×4 banks×16 bits) as a whole.

A detailed read operation of the DDR SDRAM is as follows. The respectivesignals of the chip select /CS, /RAS and /CAS and write enable /WE areinputted in synchronism with the CLK signal. A row address and a bankselect signal are inputted simultaneously with /RAS=0 and held in therow address buffer 205 and the bank select circuit 212 respectively. Therow decoder 210 for the bank designated by the bank select circuit 212decodes a row address signal and hence the corresponding memory cellarray 200 outputs row overall data as a small signal. The outputtedsmall signal is amplified by and held in the corresponding senseamplifier 202. Thus, the specified bank is rendered active (Active).

After 3 CLKs since the input of the row address, a column address and abank select signal are inputted simultaneously with CAS=0 andrespectively held in the column address buffer 206 and the bank selectcircuit 212. If the specified bank is active, then the held columnaddress is outputted from the column address counter 207 and thecorresponding column decoder 203 selects a column. The selected data isoutputted from the sense amplifier 202. The data outputted at this timecorresponds to two pairs or sets (8 bits in ×4-bit configuration and 32bits in ×16-bit configuration).

The data outputted from the sense amplifier 202 is outputted from thedata output circuit 211 to the outside of the chip through a data busDataBus. Timing provided to output it is synchronized with both therising and falling edges of QCLK outputted from the DLL 214. At thistime, the two pairs of data are parallel-to-serial converted into dataof one pair×two as described above. Simultaneously with the output ofthe data, the DQS buffer 215 outputs a data strobe signal DQS therefrom.When the burst length stored in the mode register 213 is 4 or more, thecolumn address counter 207 automatically increments addresses to readout the next column data.

The DLL 214 plays a role in producing an operating clock for the dataoutput circuit 211 and the DQS buffer 215. In the data output circuit211 and the DQS buffer 215, time is required between the input of theinternal clock signal generated by the DLL 214 thereto and the output ofthe data signal and the data strobe signal therefrom. Therefore, asuitable replica circuit is used to advance the phase of the internalclock signal ahead of the external CLK, thereby allowing the phases ofthe data signal and the data strobe signal to coincide with that of theexternal clock CLK. Thus, the DQS buffer is brought to an output highimpedance state except for the above data output operation.

Since the DQS buffer 215 of the DDR SDRAM is kept in the output highimpedance state upon a write operation, a data strobe signal DQS isinputted to the terminal DQS from a data processor such as amicroprocessor or the like, and write data synchronized therewith isinputted to the terminal DQS. The data input circuit 210 captures,serially as described above, the write data inputted from the terminalDQS according to a clock signal formed based on the data strobe signalinputted from the terminal DQS, converts the data into parallel form insynchronism with the clock signal CLK, followed by transfer to a memorybank selected through the data bus DataBus. Further, the data is writteninto a selected memory cell of such a memory bank.

Owing to the application of the invention of the present application tothe above-described DDR SDRAM, a semiconductor memory capable ofhigh-speed writing and reading can be configured while a memory chip isbeing reduced in size.

Operations and effects obtained from the above-described embodiments areas follows:

(1) An advantageous effect can be obtained in that in a dynamic RAMcomprising a plurality of word lines respectively connected to addressselect terminals of a plurality of dynamic memory cells, a plurality ofcomplementary bit line pairs respectively connected to input/outputterminals of the plurality of dynamic memory cells and placed indirections opposite to one another, and a sense amplifier array which issupplied with an operating voltage according to an operation timingsignal and comprises a plurality of latch circuits for respectivelyamplifying the differences in voltage between the complementary bit linepairs, common electrodes provided in opposing relationship to storagenodes corresponding to connecting points between address select MOSFETsand information storage capacitors of the plurality of dynamic memorycells provided on both sides with the sense amplifier array as thecenter are connected to one another while circuit connections in thesense amplifier array are being ensured by wiring means using the commonelectrodes, thereby making it possible to cancel out and hence greatlyreduce complementary noise developed in two plate electrodes providedwith the sense amplifier array interposed therebetween.

(2) An advantageous effect can be obtained in that since the storagecapacitors are formed above the bit lines as the dynamic memory cells inaddition to the above, the processing of wires interconnected with thesense amplifier array interposed therebetween becomes easy and hence afurther reduction in the resistance of the wiring means using the plateelectrodes themselves can be implemented.

(3) An advantageous effect can be obtained in that since the plateelectrodes other than the capacitors can be flattened in that electrodesplaced below the storage capacitors respectively take cylindrical shapesformed on inner walls of holes defined in an interlayer dielectric inaddition to the above, the patterning of the wires interconnected withthe sense amplifier array interposed therebetween becomes easy, wherebythe wiring means using the plate electrodes themselves can be furtherreduced in resistance.

(4) An advantageous effect can be obtained in that since the commonelectrodes are formed of a laminated or multilayered film obtained bystacking the common electrodes on ruthenium or TiN in addition to theabove, a sheet resistance value thereof can be lowered and complementarynoise developed in the plate electrodes can be canceled out moreeffectively.

(5) An advantageous effect can be obtained in that a precharge circuitfor supplying an intermediate voltage of the operating voltage for thesense amplifier to the complementary bit line pair, and column switchMOSFETs for connecting complementary input/output lines extended alongthe sense amplifier array and the complementary bit lines in response toa Y select signal received at their gates are provided in the senseamplifier array in addition to the above, whereby the complementary bitlines can be divided into suitable ones and the amount of signalsnecessary for the sense operation of a sense amplifier can be ensuredwhile an increase in the storage capacity is being achieved.

(6) An advantageous effect can be obtained in that in addition to theabove, the word lines are configured as a hierarchical structurecomprising a main word lines and sub-word lines divided into plural formin the direction in which the main word lines extend, the complementarybit lines are divided into plural form in their extending direction,sub-word drivers are provided in association with the divided sub-wordlines, the sense amplifier array is provided in association with thedivided complementary bit lines, the sub-word lines are assigned to themain word lines in plural form, and each of the sub-word drivers selectsone of the plurality of sub-word lines according to a signal for eachmain word line and a signal for each sub-word selection line, wherebythe amount of signals necessary for the sense operation of each senseamplifier can be ensured while an increase in the storage capacity isbeing achieved.

(7) An advantageous effect can be obtained in that in addition to theabove, a voltage corresponding to an intermediate voltage of theoperating voltage for the sense amplifier is supplied to the commonelectrodes through power supply lines formed in mesh form inclusive of aportion above each memory array in which the dynamic memory cells areformed, whereby complementary noise developed in the plate electrodescan be canceled out more effectively.

(8) An advantageous effect can be obtained in that in addition to theabove, a first metal wiring layer corresponding to the top layer formedso as to extend in a first direction, and a second metal wiring layerformed below the top layer formed so as to extend in a second directionorthogonal to the first direction are used for the mesh-like powersupply lines to thereby make it possible to form the power supply lineswithout being restricted by other wires.

(9) An advantageous effect can be obtained in that in a dynamic RAMcomprising a plurality of word lines respectively connected to addressselect terminals of a plurality of dynamic memory cells, a plurality ofcomplementary bit line pairs respectively connected to input/outputterminals of the plurality of dynamic memory cells and placed indirections opposite to one another, and a sense amplifier array which issupplied with an operating voltage according to an operation timingsignal and comprises a plurality of latch circuits for respectivelyamplifying the differences in voltage between the complementary bit linepairs, common electrodes provided in opposing relationship to storagenodes corresponding to connecting points between address select MOSFETsand information storage capacitors of the plurality of dynamic memorycells provided on both sides with the sense amplifier array as thecenter are connected to one another while circuit connections in thesense amplifier array are being ensured by wiring means using the samematerial as the common electrodes, thereby making it possible to cancelout and thereby greatly reduce complementary noise developed in twoplate electrodes provided with the sense amplifier array interposedtherebetween.

(10) An advantageous effect can be obtained in that in a dynamic RAMcomprising a plurality of word lines respectively connected to addressselect terminals of a plurality of dynamic memory cells, a plurality ofcomplementary bit line pairs respectively connected to input/outputterminals of the plurality of dynamic memory cells and placed indirections opposite to one another, and a sense amplifier array which issupplied with an operating voltage according to an operation timingsignal and comprises a plurality of latch circuits for respectivelyamplifying the differences in voltage between the complementary bit linepairs, common electrodes provided in opposing relationship to storagenodes corresponding to connecting points between address select MOSFETsand information storage capacitors of the plurality of dynamic memorycells provided on both sides with the sense amplifier array as thecenter are connected to one another while circuit connections in thesense amplifier array are being ensured by wiring means formed in thesame process step as the common electrodes, thereby making it possibleto cancel out and thereby greatly reduce complementary noise developedin two plate electrodes provided with the sense amplifier arrayinterposed therebetween.

(11) An advantageous effect can be obtained in that in a dynamic RAMcomprising a plurality of word lines respectively connected to addressselect terminals of a plurality of dynamic memory cells, a plurality ofcomplementary bit line pairs respectively connected to input/outputterminals of the plurality of dynamic memory cells and placed indirections opposite to one another, and a sense amplifier array which issupplied with an operating voltage according to an operation timingsignal and comprises a plurality of latch circuits for respectivelyamplifying the differences in voltage between the complementary bit linepairs, common electrodes provided in opposing relationship to storagenodes corresponding to connecting points between address select MOSFETsand information storage capacitors of the plurality of dynamic memorycells provided on both sides with the sense amplifier array as thecenter are connected to one another while circuit connections in thesense amplifier array are being ensured by wiring means formed with thesame layer as the common electrodes, thereby making it possible tocancel out and thereby greatly reduce complementary noise developed intwo plate electrodes provided with the sense amplifier array interposedtherebetween.

(12) An advantageous effect can be obtained in that in an open bit linetype dynamic RAM comprising a plurality of word lines respectivelyconnected to address select terminals of a plurality of dynamic memorycells, a plurality of complementary bit line pairs respectivelyconnected to input/output terminals of the plurality of dynamic memorycells and placed in directions opposite to one another, and a senseamplifier array which is supplied with an operating voltage according toan operation timing signal and comprises a plurality of latch circuitsfor respectively amplifying the differences in voltage between thecomplementary bit line pairs, power supply lines are provided in meshform inclusive of a portion above each memory array in which the dynamicmemory cells are formed, thereby reducing noise developed in each plateelectrode supplied via each power supply line with a voltagecorresponding thereto, a substrate and selection and non-selectionlevels of each word line, whereby an operating margin forone-intersection DRAM array can greatly be increased while highintegration by the one-intersection DRAM array is being exploited.

(13) An advantageous effect can be obtained in that in addition to theabove, the word lines are configured as a hierarchical structurecomprising main word lines and sub-word lines divided into plural formin the direction in which the main word lines extend, the complementarybit lines are divided into plural form in their extending direction,sub-word drivers are provided in association with the divided sub-wordlines, the sense amplifier array is provided in association with thedivided complementary bit lines, the sub-word lines are assigned to themain word lines in plural form, and the sub-word driver selects one ofthe plurality of sub-word lines according to a signal for each main wordline and a signal for each sub-word selection line, whereby the amountof signals necessary for the sense operation of each sense amplifier canbe ensured while an increase in the storage capacity is being achieved.

(14) An advantageous effect can be obtained in that in addition to theabove, each of the power supply line is configured so as to supply anoperating voltage corresponding to the non-selection level of thesub-word line to the sub-word driver, whereby the sub-word line can beprevented from floating, and the time required to hold information byeach memory cell can be ensured.

(15) An advantageous effect can be obtained in that in addition to theabove, each of the power supply lines is configured so as to supply anoperating voltage corresponding to the selection level of the sub-wordline to the sub-word driver, whereby the selection level of eachsub-word line can be ensured and the full writing of information chargeinto each memory cell can be ensured, thereby making it possible toensure an information holding time as a result thereof.

(16) An advantageous effect can be obtained in that in addition to theabove, each of the power supply lines is set to a predetermined voltagesupplied to each of the common electrodes provided in opposingrelationship to the storage nodes for the storage capacitors, therebymaking it possible to cancel out complementary noise developed in thetwo plate electrodes provided with the sense amplifier array interposedtherebetween.

(17) An advantageous effect can be obtained in that in addition to theabove, each of the power supply lines is configured so as to supply asubstrate bias voltage to a semiconductor region in which the addressselection MOSFETs of the dynamic RAM are formed, thereby making itpossible to stabilize a substrate voltage and reduce noise placed oneach bit line or the like through a capacitance parasitic on thesubstrate.

The invention, which has been made by the present inventors, has beendescribed above specifically by the embodiments. However, the inventionof the present application is not necessarily limited to theembodiments. It is needless to say that various changes can be madethereto within the scope not departing from the its substance. Forexample, a substrate (P type well) itself on which a pair of sub arraysprovided with a sense amplifier array interposed therebetween is formed,is used to form such a slit structure that wires suitably penetrate thesense amplifier array, and they may be interconnected with one anotherby a semiconductor region related to it. An input/output interface of adynamic RAM is not limited to the above-described DDR SDRAM. Variousembodiments such as an SDRAM, etc. can be adopted. The present inventioncan be widely used in an open bit line type dynamic RAM and asemiconductor device.

Advantageous effects obtained by a typical one of the inventionsdisclosed in the present application will be described briefly asfollows: In a dynamic RAM comprising a plurality of word linesrespectively connected to address select terminals of a plurality ofdynamic memory cells, a plurality of complementary bit line pairsrespectively connected to input/output terminals of the plurality ofdynamic memory cells and placed in directions opposite to one another,and a sense amplifier array which is supplied with an operating voltageaccording to an operation timing signal and comprises a plurality oflatch circuits for respectively amplifying the differences in voltagebetween the complementary bit line pairs, common electrodes provided inopposing relationship to storage nodes corresponding to connectingpoints between address select MOSFETs and information storage capacitorsof the plurality of dynamic memory cells provided on both sides with thesense amplifier array as the center are connected to one another whilecircuit connections in the sense amplifier array are being ensured bywiring means using the common electrodes, thereby making it possible tocancel out and hence greatly reduce complementary noise developed in twoplate electrodes provided with the sense amplifier array interposedtherebetween.

1. A dynamic RAM, comprising: plurality of dynamic memory cells eachcomprising a MOSFET and a capacitor, said MOSFET having a gate set as aselect terminal, one source and drain set as input/output terminals, andthe other source and drain connected to storage nodes of the capacitor;plurality of word lines respectively connected to the select terminalsof the plurality of dynamic memory cells; plurality of complementary bitline pairs respectively connected to the input/output terminals of theplurality of dynamic memory cells; and sense amplifier array comprisinga plurality of latch circuits which respectively amplify differences involtage between the complementary bit line pairs placed so as to extendin directions opposite to each other from each pair of input/outputterminals; and wherein power supply lines are provided in mesh forminclusive of a portion above a memory array in which the dynamic memorycells are formed or a portion above word drivers or sense amplifiers areformed.
 2. The dynamic RAM according to claim 1, wherein said word linescomprise main word lines and sub-word lines divided into plural form inthe direction in which the main word lines extend, sub-word drivers areprovided so as to correspond to the divided sub-word lines, saidsub-word lines are assigned to said each main word line in plural form,and said each sub-word driver selects one of the plurality of sub-wordlines in response to a signal on the main word line and a signal on asub-word select line.
 3. The dynamic RAM according to claim 1, furtherincluding word drivers connected to the plurality of word lines, andwherein said each power supply line supplies an operating voltagecorresponding to a non-selection level of said each word line to saidword driver.
 4. The dynamic RAM according to claim 1, further includingword drivers connected to the plurality of word lines, and wherein saideach power supply line supplies an operating voltage corresponding to aselection level of said each word line to said word driver.
 5. Thedynamic RAM according to claim 1, wherein said each power supply linesupplies a voltage to be applied to each of common electrodes providedin association with the storage nodes of the capacitors.
 6. The dynamicRAM according to claim 1, wherein said each power supply line supplies asubstrate bias voltage to a semiconductor region on which MOSFETsconstituting the dynamic memory cells are formed.
 7. A semiconductordevice, comprising: a first memory mat including a plurality of firstbit lines, a plurality of first word lines, and a plurality of firstmemory cells respectively connected to the plurality of first bit linesand the plurality of first word lines; a second memory mat including aplurality of second bit lines, a plurality of second word lines, and aplurality of second memory cells respectively connected to points wherethe plurality of second bit lines and the plurality of second word linesintersect; and a plurality of sense amplifiers formed in a regionbetween said first memory mat and said second memory mat; wherein eachof said plurality of sense amplifiers is connected to a correspondingone of the plurality of first bit lines and a corresponding one of theplurality of second bit lines, each of the plurality of first memorycells includes a first capacitor having first and second electrodes, anda first transistor having a gate coupled to a corresponding one of theplurality of first word lines and a source to drain path whose one iscoupled to a corresponding one of the plurality of first bit lines andwhose other is connected to the first electrode of the first capacitor,and each of the plurality of second memory cells includes a secondcapacitor having third and fourth electrodes, and a second transistorhaving a gate coupled to a corresponding one of the plurality of secondword lines and a source to drain path whose one is coupled to acorresponding one of the plurality of second bit lines and whose otheris coupled to the fourth electrode of the second capacitor; a pluralityof first voltage wires which are formed in a first layer on the firstmemory mat, the second memory mat and the sense amplifiers and extend ina first direction; or on the first word drivers adjacent to the firstmemory mat, the second word drivers adjacent to the second memory matand the sense amplifiers and extend in a first direction; and aplurality of second voltage wires which are formed in a second layer onthe first layer, extend in a second direction different from the firstdirection, and are respectively coupled to the plurality of firstvoltage wires by a portion for connecting between the first layer andthe second layer.